Automated filler and lever controller for liquid nitrogen

ABSTRACT

A system of supplying a liquid to a relatively small use vessel, such as a point of use inside an instrument, from a relatively large supply vessel remote from the use vessel, such as a large flask external to the instrument. The invention comprises a fluids conduit system controlled by a circuit operated by changing liquid level in the use vessel to pressurize the supply vessel to thereby flow liquid over to the use vessel. The circuit includes an RC portion to set the length of time that liquid flows.

limited mates Patet yers et a1.

[ AUTOMATED FllLLER AND LEVER CONTROLLER FOR LIQUID NITROGEN [75]Inventors: Robert E. Byers, New Kensington;

John Schmitt, Jeannette, both of Pa.

[73] Assignee: Gulf Research & Development Company, Pittsburgh, Pa.

221 Filed: June 27,1972

21 Appl.No.:266,536

[52] US. Cl 137/212, 137/213, 137/392 [51] Int. Cl B67d 5/54 [58] Fieldof Search 141/94, 95, 96, 192, 193,

[56] References Cited UNITED STATES PATENTS 1.843.363 2/1932 Henes137/212 3.014.481 12/1961 Rumble et a1. 137/212 FROM 5/ -/1uX/. /A/z QSUPPLY Mar. 19, 1974 3,279,379 10/1966 Klyce 137/392 3,340,892 9/1967Holland 137/392 3,670,765 6/1972 Haynes 137/392 FOREIGN PATENTS ORAPPLICATIONS 689,075 6/1964 Canada 137/392 915,948 l/l963 Great Britain137/392 Primary Examiner-Houston S. Bell, Jr.

[ 5 7 ABSTRACT A system of supplying a liquid to a relatively small usevessel, such as a point of use inside an instrument, from a relativelylarge supply vessel remote ilrom the use vessel, ic h as a large flaskexternal to the instrument. The invention comprises a fluids conduitsystem controlled by a circuit operated by changing liquid level in theuse vessel to pressurize the supply vessel to thereby flow liquid overto the use vessel. The circuit includes an RC portion to set the lengthof time that liquid flows.

8 Claims, 3 Drawing Figures PATENTEI] MR 1 1 SHEEI 2 BF 2 AUTOMATEDFILLER AND LEVER CONTROLLER FOR LIQUID NITROGEN This invention relatesto apparatus for maintaining a level of a liquid in a vessel, and isparticularly adapted for use in instrumentation using liquid nitrogenwherein a predetermined level of liquid nitrogen must be maintained in arelatively small vessel inside the instrument.

The invention was developed specifically for use with the commercialinstrument made by American Instrument Company of Silver Spring, Md. andcovered by U. S. Pat. Nos. 3,059,478 to Coggeshall et al., and 3,295,720to T. J. Sloan. The Coggeshall patent covers the basic system, and theSloan patent relates to an improved control system. In that instrument,liquid nitrogen is transferred from a small internal storage vessel to astill smaller sample or use vessel, and the nitrogen in the samplevessel must be maintained at some predetermined level. The problem isthat the size of the internal storage vessel prohibits continuous testsof long duration, on the order of 72 hours for example, because thenitrogen in the internal storage vessel exhausts too quickly. Referencemay be had to the above identified Coggeshall patent in which FIG. 1shows the overall system and reference numeral 32 is the sample or usevessel.

Liquid nitrogen can be purchased in standard large capacity flasks.Broadly, the invention provides means to connect such large standardcommercial flasks, which contain sufficient volume of liquid nitrogenfor tests of any duration which may be encountered, directly to thesample or use flask inside the instrument. The prior relatively smallinternal storage flask with its attendant problems and disadvantages isthus completely eliminated. Heretofore, it was necessary to open theinstrument and periodically refill the small internal storage flask, andthen reassemble the parts and the instrument. Further, the procedureheretofore available is inherently undesirable, and further has adisadvantage that it does not permit the running of long duration tests.With the present invention, only one external connection must be madebetween the instrument and the commercial flask, thus eliminating theneed to dissassemble the instrument, while Simultaneously P ittin r nraqf 99s .tt

More broadly, the invention could be used in any environment wherein itis desired to move a liquid from a storage vessel to a use vessel, inwhich use vessel a predetermined level must be maintained. Anotherapplication of the invention couldbe in handling toxic and/or corrosiveliquids wherein it is desired to minimize the possibility of humancontact with such liquids. Liquid nitrogen, of course, boils at atemperature well below room temperature, and in any case some nitrogenwill be gaseous in order to fill the vessel, and therefore the largestorage vessel will have within it a two phase system. The gas in thestorage vessel above the liquid is helpful in driving the liquid to theuse vessel. However, the invention also provides an auxiliary drivinggas, and, if the invention should be used with a liquid which does notboil at about room temperature, then the auxiliary driving gas alonewill be sufficient to drive such liquid. Such other liquids mightrequire a change in the level detection means. Depending upon theparticular application, any conventional device m shtrbss s i slu t s sa tixittrslsn photo cell, pressure switch, or the like. I

Various other schemes have been tried in the prior art to accomplishthis goal of providing relatively large capacity liquid storage vesselsexternal to the instrument being serviced or other point of use. Onesuch system includes a heater in the equivalent of the large externalsupply vessel to thereby cause an increase in gas pressure above theliquid. This scheme suffers from the apparent problems of having to dealwith thermodynamic forces which could become tricky and difficult,mechanical difficulties in making a small heater, and moving such aheater into and out of the main supply vessel.

The invention also provides an electrical circuit driven primarily by alevel sensing device in the use vessel to control the flow from thesupply vessel to the use vessel. The circuit provides means to stop theventing of boil off gas from the supply vessel and to simultaneouslycommence flow of driving gas from an auxiliary supply. The circuit alsoincludes means to determine the length of time during which liquid willbe driven over from the supply vessel to the use vessel, and furtherprovides means to easily change this predetermined time. This portion ofthe circuit comprises a resistance/capacitance (RC) network to controlthe firing of a transistor to thereby operate a relay which in turnstops the flow. A variable resistance is included in the RC circuit tocontrol the charging of the capacitor which controls the length of timerequired for the transistor to fire. The circuit also includes the meansto control the timing and sequence of the various steps and operationswhich occur during a cycle of driving liquid over from the supply vesselto the use vessel.

Another feature of the invention is the inclusion of a control vent onthe safety bleed from the supply vessel. This is an easily made pin holetype of device fitted onto the normal opening of the vent controllingsolenoid valve.

The above and other advantages of the invention will be pointed out orwill become evident in the following detailed description and claims,and in the accompanying drawing also forming a part of the disclosure,in which:

FIG. l is an elevational view of an apparatus embodying the inventionwith some parts shown diagrammatically and other parts broken away andin cross-section;

FIG. 2 is a view of the bleeder vent; and

FIG. 3 is a schematic diagram of the electrical control circuit.

Referring now in detail to the drawing, reference numeral 10 designatesa wall of an instrument which contains a vessel l2'within itself. Vessel12 corresponds to the dewar flask32 in FIG. 1 of the Coggeshall patentidentified above. More generally, vessel 12 represents any use vessel inwhich it is desired to maintain a predetermined level of a liquid 14. Amovable shelf 16 in the instrument supports the vessel 12, and anotherwall 18 The commercial instrument includes level sensing means 22mounted in lid 20, and these same means 22, unchanged, are used in thepresent invention, and thus are not shown or described in detail. Levelsensing means 22 includes a thermistor which actually contacts theliquid 14 in the vessel 12, and a transistor circuit, not shown, whichfunctions effectually like a switch in the circuitry of FIG. 3. Thethermistor is indicated by the black dot at the end of physical sensingmeans 22,

' and the electrical capability of the level sensing means 22 isindicated by the symbol for a normally open switch in FIG. 3. In otherenvironments, other liquid level sensing means could be used.

Means are provided to prevent splashing of the liquid nitrogen as itenters the use vessel. To this end, a length of plexiglas pipe or tube24 is mounted in another opening in the lid 20 by any suitable means andextends downwardly therefrom into the liquid 14 in the vessel 12. Alength of conventional specially constructed long vacuum type insulatedglass tubing 26 extends from the wall to the upper end of perforatedtube 24.

Means are provided to connect tubing 26 to the inside of wall 110, andto connect an end of a similar transfer tube 28 to the opposite sideofthe wall, with the liquid carrying openings in the two tubes 26 and 28in communication with each other. To this-end, a pair of I ings in theother plate 30. Conduit 29 is held by the two plates 30, and it is thisconduit which serves as the connection between tubing 26 on the insideof wall 110 and tubing 28 on the outside of the wall. A short length ofmetal tubing 36 is joined to the inside end of conduit 29 by anysuitable means such as soldering, and the opposite end of tubing 30 isjoined to insulated tubing 26 by a suitable glass-to-metal seal 31. Atthe opposite outside end of conduit 29, the capability of making a quickconnection and disconnection between the transfer tube 28 and thisconduit is provided by means of mating flanged ends with an O-ring 33fitted therebetween, and is finally completed by means of a suitableflange clamp, not shown. This kind of connection is known as an O-ringjoint in the art.

' rhevesserss is a aapwiiam of commerce in which liquid nitrogen issold. Typically, it is a metal vacuum construction vessel, of 50 literscapacity, with outside dimensions of approximately inches diameter and30 inches high. An adapter 36 is put into the neck of the supply vessel.Gasketing material, not shown, of any suitable type may be providedbetween adapter 36 and vessel 34.

V "Tii'e'"6';soite end of the insulated liquid nitrogen tube 28 extendsthrough the adapter 36 and has a long snorkel inlet tube 38 whichterminates in closely spaced relation to the bottom of the supply vessel34 in order to be able to deliver substantially all of the liquid in thevessel 34. Adapter 36 further includes the tube 40 which branches offinto a pair of tubes 42 and 44. The flow in tube 42 from the auxiliarysupply (not shown) into the vessel 34 above the liquid therein iscontrolled by a normally closed solenoid valve labelled 811. In asimilar manner, the flow of gaseous nitrogen in tube 44 out of thevessel 34 for venting purposes is controlled by a normally open solenoidvalve labelled S2. Th SQAQ Q EQXELWtfil spsfiz. are. themselvesconventional. The outer end'of the vent tube 44 is provided with a ventbleed 'device 46, shown in more detail in 'operated. The line 74 FIG. 2.

Basically, this device comprises a standard pneumatic fitting havingthreads 48 at one end, and a nipple 50 at the opposite end. The nipple50 is modified by the addition of an end plate, as by welding orsoldering, which plate is provided with an opening 52 of relativelysmall diameter. In the successfully constructed embodiment, the hole 52was on the order of one thirty-second of an inch in diameter. Thepurpose of the bleeder 46 with its pin hole 52 is to slow down the rateat which the nitrogen escapes from the supply vessel 34, to thereby evenfurther lengthen the time between required refills of the main nitrogensupply vessel 34. In other applications, a needle valve or the likecould be provided in place of bleeder 46 to further control venting;

blocking such a gravity flow. In other environments,

when dealing with substances which are liquid at room temperature, thispotential problem can be easily avoided by locating vessel 12 higherthan the supply vessel.

The circuit 54 is built on a hot or supply line 56 and a ground line 58.Direct current from a suitable source not shown, was used to operate thevarious coils. .A main on/off switch is provided in line 56. The coil ofthe solenoid valve S1 is located in a line 60 which is connected to theground line 58 at one end and terminates at a junction point 62. A line64 containing the first set of contacts 66-1 on a double manual switchconnects point 62 to the hot line 56. The second set of contacts 66-2 ofthis switch is in a line 68 in series circuit with the coil of thenormally open solenoid valve S2. Operation of switch 66 will open thenormally closed solenoid valve S1 and will close normally open solenoidvalve S2 to override the automatic circuitry described below in theevent it should be desired to supply liquid from supply vessel 34 to usevessel 12 at a time other than when the circuitry indicates that liquidsupply is required. The double switch 66 is primarily used for start-up.

A line 70 extends from supply line 56 to a point 72 and contains theswitch or switch-like part of level sensing device 22 which functions asan open switch in normal operation. That is, switch 22 closes andsupplies power to point 72 only when liquid is required in vessel 12,and otherwise keeps the remaining circuitry inactive so long as theliquid in vessel 12 is at or above the predetermined level.

Three lines 74, 76, and 78 branching from point 72 contain the remainingcircuitry. Line 74 contains a pair of normally closed contacts 82 on arelay R1 and a diode 84 biased as shown. The diode 84 serves toprocurrent when manual switch contacts thereafter terminates at point 62described above. Line 76 contains a pair .of normally closed contacts 86on the relay R1 and terminates at a point 88. A variable resistancedevice or potentiometer 90 is connected to point 88 and to a line 92which contains a capacitor C1, and which finally terminates at theground line 58. A unijunction transistor 94 has one tertect transistor94 from a direct connection to line 66-1 are minal connected by a line96 to the line 92 between potentiometer 90 and capacitor C1, and asecond terminal connected by a line 98 to the point 88. Line 98 containsa resistor 100 which normally provides a reverse bias on transistor 94.The last line 78 contains, in series circuit from left to right, a diode102, a junction point to jumper line 80, a pair of normally opencontacts 104 on relay R1, a resistor 106, a connecting point to a line108 to the third terminal on transistor 94, and the coil of relay R1.The jumper line 80 connects to line 68 between the two elements therein.The diode 102 serves the same function as diode 84 but with respect toswitch contacts 66-2. The resistor 106 is current limit ing because theR1 relay coil must be low resistance in order to be in line 78 in thesame circuit with transistor 94, which, of course, is a low currentdevice. The three terminals of the transistor 94 are connected to thelines 96, 100 and 108 and are called, respectively, emitter, base 2, andbase 1.

OPERATION Looking at FIGS. 1 and 3 of the drawing simultaneously, theoperation of the invention can best be understood by setting forth onecycle of the fill or liquid transfer operation. Various different thingsoccur at various different times, the sequence being controlled by thecircuit 54. FIG. 3 shows the apparatus at a stable condition, i.e., theliquid in vessel 12 is at or above device 22 and thus the contacts ofdevice 22 is open thereby rendering the subsequent circuitry inactive.

A cycle begins when the level in vessel 12 falls and the device 22effectively conducts. The first occurences are that the two solenoidvalves S1 and S2 operate to thereby stop venting the supply vessel 34via line 44 and to supply driving force in the form of gas underpressure from the auxiliary supply via line 42. Solenoid S1 opensbecause normally closed contacts 82 in line 74 on relay R1 remain intheir normally closed state thus connecting now activated point 72 toground via the coil S1. The coil of solenoid valve S2 is activated atonce via lines 78, 80 and 68, to close this normally open valve to stopventing.

Nitrogen was used and is preferred over air for the auxiliary gas drivein the successfully constructed embodiment because service air oftencontains moisture. Water in the main supply vessel 34 will change theboiling point of the nitrogen therein, and this change in boiling pointhas a deleterious effect on the operation of the instrument of theCoggeshall patent. However, more generally, in other environments, anygas may be used as the auxiliary drive, including air, so long as thenature of the particular environment is such as to permit the use ofthat particular gas.

The next occurrence in the sequence is the firing of the transistor 94to activate the coil of the relay R1 via the lines 108, 96 and 76 andback to the activated point 72. The length of time required for thetransistor to become conducting across the lines 96 and 100 is thelength of time during which liquid will be driven over from vessel 34 tovessel 12 because of the operation of the two solenoid valves, asdescribed above. Variable resistance 90 and capacitor C1 determine thislength of time in the usual manner of an RC circuit. Current leakagethrough the resistor 90, the rate of which is controlled by the settingthereon, slowly charges capacitor C1 until the voltage increases to thepoint at which the transistor via the line 96 fires. The emitter voltagebuilds up at 96 until the reverse bias on line 98 is overcome, at whichmoment the device 94 becomes forwardly biased and current flows vialines 96 and 108 (basel) and to coil R1.

The next three occurrences happen simultaneously upon firing oftransistor 94. They are, first the establishment of a holding circuitfor relay R1 via closing of contact 104 in line 78; secondly, cessationofthe supply of driving gas because of the opening of normally closedcontacts 82 on the relay R1 in the line 74 to thereby deactivate coilS1; and finally, deactivation of the Re circuit via opening of thenormally closed contacts 86 in the line 76. Note that the solenoid valveS2 remains closed thus holding the main supply vessel 34 sealed in theinterim between the end of the third group of occurrences and thebeginning of the fourth and last group of occurrences thus to preventgaseous nitrogen resulting from natural boiling in tube 28 frominterrupting the flow of the liquid nitrogen later.

The final set of occurrences are caused by the arrival of the liquid upto the predetermined level in the vessel 12 to thereby cause contacts 22to return to their open condition. When contacts 22 open again, thecoils of relay R1 and solenoid valve S2 in the lines 78 and 68 becomedeactivated. The system and circuit have now completed a fill cycle andthe circuit has returned to the FIG. 3 configuration.

An advantage of the circuit of FIG. 3 is that it automatically providesfor shut-off in the event the level in use vessel 12 should reach thepredetermined height prior to the expiration of the RC determined timeand accompanying firing of transistor 941. In this event the last set ofoccurrences happens at once, S1 returns to its normally closedcondition, and no further positive drive occurs. In either case, acertain amount of coasting will occur after S1 closes and before S2re-opens because of the trapped gas pressure above the liquid in supplyvessel 34. This phenomenon is an advantage because, together with thebleeder, it consumes the auxiliary gas supply, and it reduces the numberof fill cycles per unit time thereby conserving the liquid nitrogen. Thecoasting causes a tailing off in the supply rather than a sharp cut-off,thus enhancing the above advantages and providing smoother operation.

While the invention has been described in detail above, it is to beunderstood that this detailed description is by way of example only, andthe protection granted is to be limited only within the spirit of theinvention and the scope of the following claims.

We claim:

1. Apparatus for flowing liquid from a supply vessel to a use vessel fora predetermined length of time, comprising means to supply pressurizedgas to said supply vessel above the liquid therein, means to flow liquidout of said supply vessel under the influence of said pressurized gas,means to sense when said liquid falls below a predetermined level insaid use vessel, circuit means operated by said sensing means, saidcircuit means including means to commence the supply of said pressurizedgas to said supply vessel upon operation of said sensing means, and saidcircuit means including adjustable means to control the length of timepressurized gas is supplied to the upper end of said supply vessel andto thereafter stop the flow of pressurized gas to said supply vessel.

2. The combination of claim 1, wherein said liquid is id q maqs pq us is .msanatq. YQntPP gaseous nitrogen from the upper end of said supplyvessel, and means to close said vent means when said pressurized gassupply means are operative.

3. The combination of claim 2, in which said vent means include pin-holebleeder means on said vent means to reduce the rate and amount ofboil-off gaseous nitrogen leaving said supply vessel.

4. The combination of claim 1, in which said means to flow liquid out ofsaid supply vessel comprise a snorkel tube extending down to a positionclosely adjacent the bottom of said supply vessel, whereby substantiallyall of the liquid in said supply vessel will be flowed to said usevessel.

5. The combination of claim 1, in which said sensing means comprisingmeans to activate and de-activate portions of said circuit means whensaid device does not sense and does sense said liquid in said usevessel.

6. The combination of claim 1, in which said means in said circuit meansto time and stop the How of pressurized gas to said supply vesselcomprise a unijunction transistor and an RC timing circuit so arrangedthat the charging time of said RC circuit controls the firing of saidtransistor, a variable resistance in' said RC circuitfa normally closedsolenoid valve controls the flow of said pressurized gas to the upperend of said supply vessel, and wherein said unijunction transistorcontrols said normally closed solenoid valve.

7. The combination of claim 6, wherein said liquid is liquid nitrogen,and including means to vent boiloff gaseous nitrogen from the upper endof said supply vessel, means to close said vent means when saidpressurized gas supply means are operative, a relay in said circuitmeans, said relay including a first pair of normally closed contacts inseries circuit with the coil of said normally closed solenoid valve,said relay including a second pair of normally closed contacts tocontrol the charging of said RC circuit, and wherein the firing of saidtransistor operates the coil of said relay.

8. The combination of claim 7, in which said relay includes a pair ofnormally open contacts in series circuit with said relay coil toestablish a holding circuit for said relay coil.

1. Apparatus for flowing liquid from a supply vessel to a use vessel fora predetermined length of time, comprising means to supply pressurizedgas to said supply vessel above the liquid therein, means to flow liquidout of said supply vessel under the influence of said pressurized gas,means to sense when said liquid falls below a predetermined level insaid use vessel, circuit means operated by said sensing means, saidcircuit means including means to commence the supply of said pressurizedgas to said supply vessel upon operation of said sensing means, and saidcircuit means including adjustable means to control the length of timepressurized gas is supplied to the upper end of said supply vessel andto thereafter stop the flow of pressurized gas to said supply vessel. 2.The combination of claim 1, wherein said liquid is liquid nitrogen,means to vent boil-off gaseous nitrogen from the upper end of saidsupply vessel, and means to close said vent means when said pressurizedgas supply means are operative.
 3. The combination of claim 2, andpin-hole bleeder means on said vent means to reduce the rate and amountof boil-off gaseous nitrogen leaving said supply vessel.
 4. Thecombination of claim 1, said means to flow liquid out of said supplyvessel comprising a snorkel tube extending down to a position closelyadjacent the bottom of said supply vessel, whereby substantially all ofthe liquid in said supply vessel will be flowed to said use vessel. 5.The combination of claim 1, said sensing means comprising means toactivate and de-activate portions of said circuit means when said devicedoes not sense and does sense said liquid in said use vessel.
 6. Thecombination of claim 1, said means in said circuit means to time andstop the flow of pressurized gas to said supply vessel comprising aunijunction transistor and an RC timing circuit so arranged that thecharging time of said RC circuit controls the firing of said transistor,a variable resistance in said RC circuit, a normally closed solenoidvalve to control the flow of said pressurized gas to the upper end ofsaid supply vessel, and wherein said unijunction transistor controlssaid normally closed solenoid valve.
 7. The combination of claim 6,wherein said liquid is liquid nitrogen, means to vent boil-off gaseousnitrogen from the upper end of said supply vessel, means to close saidvent means when said pressurized gas supply means are operative, a relayin said circuit means, said relay including a first pair of normallyclosed contacts in series circuit with the coil of said normally closedsolenoid valve, said relay including a second pair of normally closedcontacts to control the charging of said RC circuit, and wherein thefiring of said transistor operates the coil of said relay.
 8. Thecombination of claim 7, said relay including a pair of normally opencontacts in series circuit with said relay coil to establish a holdingcircuit for said relay coil.